School of Dragons have put together some resources to help students understand how to design a scientific experiment. An experiment should have the following parts:
A question that the scientist is trying to answer (Asking the Right Question)
A hypothesis (Practice Writing Hypotheses)
Analysis & conclusion (How to Write an Experimental Conclusion)
For the format of the hypothesis, I have students focus on adding because to the if-then statement, in order to explain their thinking about why they think the first thing will change the second.
For practice writing procedures, I have students write step-by-step procedures on how to create the perfect sandwich, which they make out of paper. Teammates assemble the sandwich while following the procedures very literally.
For data collection, we take a class poll to determine each classes favorite movies. Students generate recommendations on the back whiteboard. They then vote for movies that they each like (no limit). After totals are collected, each team builds a graph/chart as a team, based upon a random assignment (line graph, bar graph, pictograph, pie chart/graph). Students vote to decide which one clearly describes the classes favorite movies the fastest. The next day, each individual student builds a bar chart that combines the favorite movies from all three(+) classes. Students also practice a pie chart, indicating the slice that represents the all time favorite movie.